Microbial Biofertilizers: Mechanisms, Agricultural Applications, Innovations, and Future Perspectives
Unsustainable agricultural practices and overreliance on chemical fertilizers have led to severe environmental issues, such as soil and water pollution, loss of biodiversity, and risks to human and animal health. Moreover, plant diseases continuously decrease crop productivity and threaten global food security. Therefore, there is a strong need to focus on sustainable agricultural practices. Microbial biofertilizers emerge as environment-friendly alternatives to chemical fertilizers that help in nutrient solubilization and availability, soil fertility, and plant growth promotion, in addition to curbing the application of chemical fertilizers. Microbial inoculants enhance agricultural yield by performing complementary roles, such as facilitating nutrient uptake through biological nitrogen fixation and phosphate solubilization, promoting plant growth via phytohormone synthesis, and mitigating diseases by activating plant defense responses. A 2025 meta-analysis of 107 field studies in China reported mean yield increases of 22.3% in wheat, 13.6% in rice, 12.8% in maize, and 65.4% in millet, while a field study in saline soil reported a 25% reduction in NPK fertilizer use in barley without reducing the grain yield. This review provides an overview of the major types of microbial biofertilizers, their modes of action, and their use in important cropping systems. Special emphasis is placed on microbial consortia that can enhance nutrient cycling, plant productivity, and tolerance to abiotic stress factors. The application of nanotechnology, genetically engineered microorganisms, and combinations of microbial inoculants with organic waste are some strategies that could be adopted for next-generation biofertilizer development. The review also addresses the major hurdles in the formulation, field performance, and commercialization of microbial biofertilizers. Future perspectives revolve around optimizing microbial formulations, applying advanced biotechnological tools, and developing enabling policies for the rapid adoption of microbial biofertilizers for sustainable agriculture.